Larry, the closest I've ever seen are WWII U-boats:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=390304534988
Though I think a 1:72 scale sub would work too?
http://www.scalehobbyist.com/catago...pg=1&ppp=24&sb=stocknumber&so=a&era=0,6&sc=72
I'm thinking you should use the 1/72 scale sub and cut it. Not for a waterline model, but so that its a cutaway model that would extend past the edge of your layout. Then, below the waterline, the sub would be a cutaway cross section of the model, and you could detail the sub's interior at the point where the layout ends. But, that also means detailing the subterranian bottom of your waterway.
It's hard to buy something for about $120.00 plus freight & then only use half of it.
Josh, I might have to rethink a Sub. That thing is over 4ft. long in 1/72nd scale & that's smaller than 1/87th. That would take up the whole area I'm thinking of adding on this summer. Might have to go w/a PT boat instead.![]()
Other way around, 1/72 scale is larger scale then 1/87 scale.